1. Field of the Invention
This invention relates to a substrate support mechanism and a substrate rotation device for a disc substrate having an opening at its center and in particular to a substrate rotation device preferably used when the substrate is treated in a vacuum processing apparatus such as a film forming apparatus.
2. Description of the Related Art
In recent years, the density of recording media such as a magnetic disc and optical disc has remarkably increased. Nevertheless, a variety of investigations are continued to develop high performance discs having a higher recording density and reliability, and to establish the mass production method thereof.
For example, a magnetic disc is usually composed of an aluminum or glass disc substrate having an opening and multi-layered films formed thereon of a underlayer film such as Cr, a multi-component magnetic film such as CoCrTa and a passivation film such as carbon.
In the production of such a magnetic disc, a substrate holder which supports the substrate at the outer rim with clicks travels through a series of a heating chamber, a sputtering chamber for Cr film, a sputtering chamber for a magnetic film and a plasma CVD chamber for a carbon film, to form the respective films on the substrate.
The substrate holder is placed so that the substrate faces a target or a discharging electrode when transported into the film forming chamber, and then the film formation is carried out in the condition that the substrate is at rest. For the formation of a multi-component magnetic film, an alloy target with a prescribed composition ratio is usually used and a bias voltage is applied to the substrate during sputtering to obtain a high quality magnetic film. The bias application is also indispensable to form a diamond-like carbon film as a passivation film.
In order to prepare a magnetic disc with a higher recording density and reliability, further improvement is required in the uniformity of e.g. coercive force across the substrate by increasing the uniformity of film thickness and composition ratio in addition to the improvement in the magnetic characteristic itself of the film. For example, there is known a method to improve the uniformity of film thickness, in which the arrangement and the shape of the magnets, which are disposed behind the target, are adjusted to optimize the magnet field over the target surface. Although the uniformity of the film thickness is improved, this method has a disadvantage in that the adjustment takes much time.
Then, in order to obtain a higher quality magnetic film, the constituent elements and their composition ratios of the magnetic film need to be optimized, which is however difficult so long as the conventional sputtering apparatuses are adopted. That is, a lot of alloy targets composed of various elements and composition ratios must be provided and then the film forming condition is optimized for each target. Thus, it will require much labor and a long time to determine the desired target composition. In addition, there is the case where the alloy targets cannot be prepared, depending on the composition.
In contrast, the structure of the magnetic film in which the composition ratio varies in the direction of film thickness has been proposed to suppress the long-term decreasing rate of coercive force. However, it is impossible to change the composition in the direction of thickness so long as the above-mentioned apparatus is used.
Then, the present inventors have examined a film forming method, in which, for example, a plurality of disc substrates are fixed to a large substrate holder on the circumference with a prescribed diameter, a plurality of targets are also disposed on the identical circumference, and the substrate holder is rotated so that each substrate revolves and passes under the targets. Since the targets of single element constituting the film can be used in this method, the magnetic films with various composition ratios can be easily formed by adjusting RF power supplied to respective targets. However, the magnetic film thus obtained tends to have a layered structure of respective elements; therefore the large substrate holder must be rotated at a very high speed to obtain a homogeneous film.
In the production of magnetic discs, a Cr underlayer film, a magnetic film, and a passivation film are successively formed in respective film forming chambers. Therefore, each chamber needs to have the same rotation mechanism of the large substrate holder, which makes a hard disc manufacturing system very large and expensive. Furthermore, the substrate holder becomes also complicated and expensive in such a configuration though it is desired to be simple in structure and inexpensive because the blast treatment is periodically carried out to remove films deposited on the holder
As mentioned above, the electric bias is indispensable to form a magnetic film or diamond-like carbon film. However, when a glass substrate is employed, the electric contact resistance between the substrates and clicks is large, which causes the clicks to electrically separate from the substrate in most cases, even after a Cr underlayer is formed. As the result, the uniform bias cannot be applied to whole film formation surface. This does not permit the stable and reproducible production of high quality magnetic films.
Under these circumstances, the present inventors have further examined the structures of a film forming apparatus and a substrate holder to overcome above-mentioned disadvantages of prior art, and found that the uniformity of magnetic characteristics and film thickness could be improved by using a sputtering apparatus shown in FIG. 5 and in some case by placing a film distribution correction plate between targets and a substrate. In this configuration, targets 55, 55xe2x80x2 and 55xe2x80x3 made of single element constituting the magnetic film are disposed over the substrate 100, which is rotated around its central axis. It was also found that the configuration of FIG. 5 makes it possible to form magnetic films of various composition ratios and magnetic films whose composition varies in the direction of the film thickness.
In the formation of such films, a substrate rotation device is required which receives a substrate from a substrate holder transported into the film forming chamber and rotates the substrate facing the targets as shown in FIG. 5. And in order to prevent the enlargement of the film forming chamber, the space for transferring a substrate between the substrate holder and the substrate rotation device should be as small as possible. Therefore, the mechanism is desired to transfer the substrate between the substrate holder and the substrate rotation device without moving the substrate holder. In addition, in order to increase the productivity, a substrate rotation device, which copes with simultaneous film formation on both surfaces of the substrate, is desired.
Therefore, a principal object of this invention is to provide a substrate rotation device which receives a substrate from a substrate holder transported into the chamber without moving the substrate holder, and rotates the substrate at the same position as supported by the holder.
A further object of this invention is to provide a compact substrate rotation device, which makes it possible to apply the uniform electric bias to the whole film formation surface in a series of the formation of films including a metal film. It is also an object of this invention to provide a compact substrate rotation device, which will not obstruct the simultaneous film formation on both sides of the substrate.
Another object of this invention is to provide a substrate support mechanism, which firmly and securely grips a substrate to meet the substrate rotation device of this invention.
A substrate support mechanism of this invention, which holds the inner rim of a disc substrate having an opening at its center, comprises:
a hollow cylindrical member; a central shaft disposed in the hollow portion of said cylindrical member so as to be pushed in the axial direction by a first spring, said central shaft having at one end portion a tapered portion of which diameter increases toward the end; and a plurality of radially movable members disposed on the end face of said cylindrical member, each radially movable member being pushed inwardly by a second spring and having a click to grip the inner rim of said substrate; whereby the axial motion of the said central shaft is converted to the radial motion of said radially movable members to grip and release said substrate.
Since the radially outward force is exerted on the radially movable members by the action of the first spring and tapered portion, the substrate is securely supported at the inner rim and therefore will not shake or sway during the rotation. Moreover, a substrate support mechanism can be made small in side since the support and release operations of the substrate is carried out by means of the conversion of the axial motion of central shaft to radial motion of the radially movable members.
A substrate rotation device of this invention, which receives a disc substrate having an opening at its center from a substrate holder which holds the outer rim of said substrate with clicks and rotates said substrate in a processing chamber isolated from atmosphere, comprises;
a substrate support mechanism which is composed of a first hollow cylindrical member, a central shaft disposed in the hollow portion of said first hollow cylindrical member so as to be pushed in the axial direction by a first spring, said central shaft having at one end portion a tapered portion of which diameter increases toward the end, and a plurality of radially movable members disposed on one end face of said first hollow cylindrical member, each radially movable member being pushed inwardly by a second spring and having a click to grip the substrate at the inner rim, whereby the axial motion of the said central shaft is converted into the radial direction motion of said radially movable members to grip and release said substrate; a mechanism for moving said first hollow cylindrical member in the axial direction, by which said plurality of radially movable members are inserted into the opening of said substrate to the position where said clicks become at nearly the same level as said substrate; a mechanism for moving said central shaft in the axial direction; and a mechanism for rotating said first hollow cylindrical member while the clicks of said radially movable members grip said substrate.
Only the substrate is rotated whereas the substrate holder itself is at rest in this construction, which enables to make the substrate rotation device simple and small. Furthermore, the substrate rotation device does not require the additional space to transfer a substrate or interfere with the substrate holder, a shield plate or other members in the processing chamber since the substrate is transferred from the substrate holder and is rotated at the same position as supported by the substrate holder.
Accordingly, a processing apparatus can be made compact. It is also possible to carry out the simultaneous sputtering by disposing two sets of targets over both sides of the substrate, wherein the films are formed on both surfaces of the substrate at the same time.
A substrate rotation device is also characterized in that a second hollow cylindrical member is disposed in an opening formed in a wall of said processing chamber and connected at one end face to the other end face of said first cylindrical member, a rotation seal member is disposed around said second hollow cylindrical member and connected to said wall through a first bellows, a driving shaft to move said central shaft in the axial direction is disposed in said second hollow cylindrical member so as to protrude from the other end face of said second hollow cylindrical member, and said other end face of said second hollow cylindrical member is connected to the protruding end of said driving shaft through a second bellows.
This construction is preferably applied to very high vacuum apparatuses. That is, the chamber can be maintained at high vacuum during the operations of the transfer and rotation of the substrate. This permits the formation of a variety of high quality films.
It is preferable that a substrate rotation device is constructed such that said second hollow cylindrical member is electrically insulated from said rotation seal member and a mechanism for moving said second hollow cylindrical member in the axial direction and rotating said second hollow cylindrical member so that a bias voltage is applied to the substrate through said second hollow cylindrical member during the rotation of said substrate.
As mentioned above, since the substrate is gripped at its inner rim after transported into the processing chamber, if a conductive film is formed in the previous process chamber, the clicks of the substrate support mechanism are securely connected to the conductive film. Thus, the uniform bias can be applied to the whole thin film formation surface of the substrate, which enables the stable formation of higher quality thin films.